Parametric visual system indicator



May 3, 1966 M. W. WINDSOR PARAMETRIC VISUAL SYSTEM INDICATOR 2 Sheets-Sheet 1 Filed Feb. 4. 1960 FIG.

FIG. 4.

INVENTOR. MAURICE W. WINDSOR ATTORNEY.

May 3, 1966 v M. w. WINDSOR 3,249,930

PARAMETRIC VISUAL SYSTEM INDICATOR Filed Feb. 4, 1960 2 Sheets-Sheet 2 FIG. 7.

INVENTOR. MAURICE W. WINDSOR ATTORNEY.

United States Patent 3,249,930 PARAMETRIC VISUAL SYSTEM INDICATOR Maurice W. Windsor, Redondo Beach, Calif., assignor, by mesne assignments, to Thompson Ramp Wooldridge Inc., Cleveland, Ohio, a corporation of Ohio Filed Feb. 4, 1960, Ser. No. 6,719 2 Claims. (Cl. 340-253) This invention relates to the art of parametric visual system indicators and more particularly to reliable visual indicators that provide a positive visual signal at all times by exhibiting automatic changes in color in response to changes in the system measured.

Many parametric visual system indicators currently in use indicate one condition of a system by presenting a positive visual signal and another condition by the absence of any positive visual signal. For example, an engine oil pressure indicator in many automobiles may consist of a red glass or plastic shielded light bulb that is electrically energized in response to the settings of a pressure switch. Thus, when oil pressure is low, the pressure switch contacts are closed, the light bulb is energized and a positive red visual signal is presented to the driver. When oil pressure rises to a predetermined safe value sufficient to open the pressure switch, the bulb is de-energized, thereby terminating the positive red visual signal to the driver. This absence of a positive visual signal, then, presumably indicates that the oil pressure is at a safe value for driving. However, in the event that there is a failure in the bulb itself or bulb energizing circuit, rendering it inoperative, and a simultaneous drop in the oil pressure to a value unsafe for driving, no positive visual signal of this unsafe condition is presented. The driver of the automobile, under the misapprehension that the oil pressure is at a safe value, may continue driving and thus experience serous damage to the engine.

Accordingly, it is an object of this invention to provide a parametric visual system indicator that in normal operation always provides a definitive visual signal.

It is another object of this invention to provide such a parametric visual system indicator in which the definitive visual signal changes color in response to changes in the system.

It is a further object of this invention to provide a parametric visual system indicator in which the absence of a normally present visual signal is indicative of a failure in the indicator circuitry.

The foregoing and related objects are realized in a parametric visual system indicator capable of responding to system variations by proportionally modulating the heat transfer rate to a thermochromic surface. As used herein, thermochromic refers to that characteristic of certain substances wherein the substance exhibits different colors within difler'ent temperature environments. According to the invention a parametric network is provided wherein variations in a characteristic of a system which is to be 'visually monitored'are converted into a correspondingly varying electric voltage. This voltage is applied across a member in which the resulting electric current flow through the member is converted to heat. The heating member is in juxtaposition to a thermochromic surface and as the heat output of the member varies with the electric voltage, the color of the thermochromic surface changes. The thermochromic surface is positioned to be visually observable and predetermined colors of the surface are indicative of predetermined conditions of the system characteristics.

The invention is explained in greater detail in the following specification with reference to the accompanying drawings in which:

FIGS. 1 and 2 are schematic diagrams of one embodiment of this invention utilizing radiative heat transfer to a thermochromic surface;

FIGS. 3iand 4 illustrate other embodiments of this invention utilizing radiative heat transfer to a thermochromic surface;

FIG. 5 illustrates another embodiment of this invention utilizing a radiation absorber'for heat transfer rate modulation;

FIG. 6 is a schematic diagram of an embodiment of this invention utilizing conductive heat transfer to a thermochromic surface; and

FIG. 7 is another embodiment of this invention utilizing conductive heat transfer to a thermochromic surface.

Similar reference characteristics are utilized to designate like members in the above drawings.

FIGS. land 2 are schematic representations of one embodiment of this invention as utilized (by way of example) in an automobile wherein the characteristic to be monitored is pressure and the system to be monitored is the automobile engine oil system.- A pressure switch 10 with the electrical contacts 12 and- 1=3 is connected to the engine oil system 11 of the automobile. A source of electromotive force 16, such as a battery, is connected to the contact 12. An electrical resistor 14 is connected between the battery 16 and the contact 1 3-. An ON-OFF switch 18'is provided in the circuit between the contact 13 and a heat generating member 20, which develops a heating signal. As illustrated, the heat generating member 20 is shown as an electric filament type light bulb. However, any type ofmember capable of converting electric energy to heat may be utilized as the heat generating member in this embodiment. For example, an electric resistor, an electric heating element of thecoil variety, or an electric strip heater might be utilized.

The member 20 is in juxtaposition to a shield means 22 which has a thermochromic surface portion 24. The shield 22, which is transparent to electromagnetic radiation in the visible portion of the electromagnetic spectrum, may be placed on a dashboard 26 of an automobile so as to be 'visibleto the automobile driver. The'ON- OFF switch 18 isprovided'in the circuit to render the cir-- cuit inoperative during time periods'when a visual signal is not required. Thus, the switch 18 may be interconnected, for example, to an engine ignition switch (not shown) of the automobile.

In operation, the'ONOFF switch 1-8 is closed toprovide circuit continuity between the battery 16 and the 'heat generating member 20. FIG. 1 shows the operation of the' parametric visual system indicator when the pressure in the engine oil system is low. In thiscondition, the electric contacts 12 and 13 are separated and an electric current i flows from the source of electromotive force '16, through the resistor 14 and the ON-OFF switch 18 to the heat, generating member 20 which converts'the electric energy to heat. The heat generated in member 20 is transferred by radiation to the thermochromic surface portion 24 of theshield 22. Since the heat generated by the member 20 is a function of the total electric current supplied to it, the value of the'resistance of the resistor 14 is selected so as to maintain the current i at a comparativelylow value. As a result, the thermochromic surface portion 24'is exposed to only a comparatively low temperature environment.

The thermochromic surface 24 reversibly changes color when exposed to a temperature environment above a specific critical temperature (T This critical temperature varies among the different materials that may be selected for the thermochromic surface portion 24. Table I lists several of the thermochromic substances with their corresponding critical temperature and colors above and below the critical temperature.

TABLE I In addition to the thermochromic materials that have a single critical temperature (T there are also materails that have two critical temperatures (T and T These materials can exhibit three different colors depending upon their temperature environment. A few of these materials are listed below in Table II. Such materials can be utilized in this invention to indicate three different predetermined conditions of a system characteristic. For example, in an automobile water temperature indicating system the temperature environment of the thermochromic material could be controlled so that one color, below the first critical temperature, indicates a low water temperature; a second color, between the first and second critical temperatures, indicates a safe water temperature range; and a third color, above the second critical temperature, indicates too high a water temperature.

TABLE II Thermochromic materials with two The thermochromic surface 24 may be either opaque or have some degree of transparency. In the former case the driver of the automobile sees the thermochromic surface 24 itself; in the latter case the driver sees not only the thermochromic surface 24 but also a transmitted colored light, which is effectively filtered by the thermochromic surface 24 so that the transmitted light contains essentially only wavelengths corresponding to the color of the thermochromic surface 24.

While the embodiments described in connection with FIGS. 1 and 2 show the thermochromic surface 24 on that portion of the shield 22 immediately adjacent to the heat generating member 20, other arrangements are also possible. FIG. 3 illustrates an arrangement wherein the thermochromic surface 24 is on portions of the shield 22 that are remote from the heat generating source 20. Operation of this embodiment is similar to the operation of the embodiments shown in FIGS. 1 and 2 except that in this embodiment the heat absorbed by shield 22 and conducted to thermochromic portion 24 are to be considered in selecting the components of the system.

The thermochromic material may be dispersed in the shield means itself. Such an arrangement is illustrated on FIG. 4. In this environment the electric current to the heat generating member 20 is controlled in a manner similar to that described in connection with FIGS. 1 and '2. The shield means 25 has a thermochromic material 27 dispersed therein. In this embodiment some of the light generated from the heat generating member 20 will be transmitted through the shield means 25 and the autocritical temperatures Color when Color when. Color when Thermoehromic material temperature is T0 g i t To temperature is less th T (e C greater i an O greater than Te but less than T6 1. Silver mercuric iodide, HgI AgI. Light yellow Dark orange 90 Carmine red. 2. Copper mercuric iodide, HgIgCllI- Red -70 Clliocolate 87 Black.

rown.

FIG. 2 illustrates the operation of this embodiment when the oil pressure in the engine oil system 11 rises to a predetermined value safe for driving. Under this condition the electrical contacts 12 and 13 of the pressure switch 14) are closed and there is a direct circuitbetween the battery 16 and the heat generating member 20. A current i flows through the heat generating member 20 and this current i is made appreciably greater than the current i There is a greater amount of heat generated in member 20 and, consequently, a greater net heat transfer to the thermochromic surface 24. This causes the temperature of the thermochromic surface 24 to increase to a'value above the critical temperature (T and therefore change color.

This provides a positive visual signal to the automobile driver that the oil pressure is at a value safe for driving. This positive visual signal remains, under normal conditions, until the oil pressure drops to an unsafe value, when a different visual signal, as described in connection v\with FIG. 1, is presented to the driver,

mobile driver is presented with a colored light. The color of the light is dependent upon the color of the thermochromic material 27 dispersed in shield means 25 and this provide a definitive visual signal to the automobile driver.

The parametric monitoring of the oil pressure and the direct modulation of the heat generated, as described above, is only one method of controlling the color of a thermochromic surface in response to variations in the oil pressure. FIG. 5 illustrates an embodiment of this invention in which the heat generated by the member 20 is constant, but the amount of heat transferred to the thermochromic surface 24 is modulated. When the ON- OFF switch 18 is closed, the heat generating member 20 is energized by the battery 16 and the heat output of the heat generating member 20 is maintained substantially constant. A control 30 senses the oil pressure in the engine oil system 11 and, in response thereto, properly positions a heat absorber means 28 between the thermochromic surface portion 24 and the heat generating member 20. Thus, when the oil pressure in engine oil system 11 is a value unsafe for driving, the control 30 positions the heat absorber 28 sothat a strongly absorbing portion 34 of absorber 28 is interposed between the heat generating member 20 and the thermochromic surface 24. The strongly absorbing portion 34 absorbs a comparatively great amount of radiation emitted from the heat generating member 20 and thus limits the temperature of the thermochromic surface 24 to a value less than the critical temperature (T When the oil pressure rises to a value safe for driving,

the control 30 senses this condition and positions the absorber 28 so that a weakly absorbing portion 32 of the absorber 28 is interposed between the heat generating member 20 and the thermochromic surface 24. The weakly absorbing portion 32 absorbs a comparatively small amount of the radiaton emitted by the heat generating member 20 and thus permits the temperature of the thermochromic surface 24 to increase to a value greater than the critical temperature (T This results in a change in color of the thermochromic surface 24 and thereby provides the desired positive visual signal to the automobile driver.

In the embodiments of this invention described above, heat transfer by radiation to a thermochromic surface was utilized to provide the required positive visual signal. This signal can also be provided according to another embodiment of this invention, through the utilization of heat transfer by conduction from a heat generating membar to a thermochromic surface. FIG. 6 illustrates this embodiment in the automobile engine oil pressure indicator described above. The operation of the parametric monitoring of oil pressure in an engine oil system is similar to that described in connection with FIGS. 1 and 2. In FIG. 6, however, a shield means 40, transparent to electromagnetic radiation in the visible portion of the electromagnetic spectrum, has a surface portion coated with a comparatively thick layer of thermochromic material 42. Imbedded in this thermochromic material 42 is a resistance wire 44 which, as the heat generating member, receives an electric current from the battery 16. When this electric current flowing in the resistance wire 44 is low, comparatively little heat is conducted to the thermochromic material 42 and the temperature of the thermochromic material 42 is maintained at a value less than its critical temperature. When the electric current in resistance wire 44 rises to a comparatively high value,

the heat transfer rate to the thermochromic material 44' is increased. Under this condition the temperature of the thermochromic material 42 increases to a value greater than its critical temperature and, therefore, a reversible color change occurs which provides the required positive visual signal.

FIG. 6 also shows the pattern in which the resistance wire 44 is embedded in the thermochromic material 42. It will be appreciated that there are many other patterns in which the resistance wire 44 may be wound. For example, the pattern might be a spiral or a parallel grid winding.

Another embodiment, in which heat transfer by conduction is utilized to control the temperature of a thermochromic material, is shown on FIG. 7. In this embodiment the heat generating member is in the form of an electrical strip heater 50. A thermochromic material 52 is deposited directlyupon a surface portion of the strip heater 50. The electric current flowing through the strip heater in response to, for example, changes in the oil pressure of an automobile engine oil system is controlled in a manner similar to that described in connection with FIGS. 1 and 2. A shield means is not required in this embodiment of the invention. I

Many changes could be made in the above constructions of this invention and many apparently widely different embodiments of this invention could be made without departing from the true scope thereof. Different embodiments of this invention might be in other automobile systems such as indicating headlight high-beam and lowbeam, battery charge and discharge, water temperature high and low, and the like. Other embodiments could be utilized in various aircraft systems and instrumentation systems. Therefore, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not as limiting.

Having thus described a new and improved parametric visual system indicator, what is desired to be obtained by Letters Patent is:

1. A visual indicator for indicating the condition of a system subject to variation between two given states, said indicator comprising:

a thermochromic member having a given critical temperature at which it reversibly changes from one color below said critical temperature to another color above said critical temperature;

an electric heater thermally coupled to said member;

circuit means for supplying an electric current of fixed magnitude that is sufficient to heat said thermochromic member above said critical temperature;

a heat modifying element positioned in heat intercepting relation between said heater and said member;

and means for automatically altering a condition of said element, as a function of the variations in the condition of said system between said states, to vary the transmission of heat from said heater to said member between an amount that heats said member above said critical temperature and a value that heats said member below said critical temperature.

2. Avisual indicator for indicating the condition of a system subject to variation between two given states, said indicator comprising:

a thermochromic member raving a given critical temperature at which it reversibly changes from one color below said critical temperature to another color above said critical temperature;

a heater. thermally coupled to said member and capable of heating the same above said critical temperature;

and means for automatically altering the amount of heat received by said thermochromic member from said heater as a function of variations in the condition of said system between the two given states, so as to heat said member above said critical temperature during a first state of the system and to heat said member below said critical temperature during a second state thereof;

said means including an element positioned in heat intercepting relation between said thermochromic NEIL C. READ, Primary Examiner.

BENNETT G. MILLER, ELI SAX, STEPHEN W.

CAPELLI, Examiners.

" w. K. TAYLOR, R. M. ANGUS, Assistant Examiners. 

1. A VISUAL INDICATOR FOR INDICATING THE CONDITION OF A SYSTEM SUBJECT TO VARIATION BETWEEN TWO GIVEN STATES, SAID INDICATOR COMPRISING: A THERMOCHROMIC MEMBER HAVING A GIVEN CRITICAL TEMPERATURE AT WHICH IT REVERSIBLY CHANGES FROM ONE COLOR BELOW SAID CRITICAL TEMPERATURE TO ANOTHER COLOR ABOVE SAID CRITICAL TEMPERATURE; AN ELECTRIC HEATER THERMALLY COUPLED TO SAID MEMBER; CIRCUIT MEANS FOR SUPPLYING AN ELECTRIC CURRENT OF FIXED MAGNITUDE THAT IS SUFFICIENT TO HEAT SAID THERMOCHROMIC MEMBER ABOVE SAID CRITICAL TEMPERATURE; A HEAT MODIFYING ELEMENT POSITIONED IN HEAT INTERCEPTING RELATION BETWEEN SAID HEATER AND SAID MEMBER; AND MEANS FOR AUTOMATICALLY ALTERING A CONDITION OF SAID ELEMENT, AS A FUNCTION OF THE VARIATIONS IN THE 